A common theme is often the 'opposites attract' dynamic. Since 2p Prussia might be depicted as having a more edgy or different personality compared to the regular Prussia, the contrast with the reader character can create interesting relationships.
Redemption is another theme. Sometimes, 2p Prussia might be written as a character who has some dark past or traits that the reader helps him overcome. This allows for character growth and development within the fanfiction, creating a heartwarming or inspiring story.
One common theme is the exploration of an alternative or '2p' personality. The 2p Prussia character often has different traits compared to the original Prussia, and the fic might focus on how the reader interacts with this unique version. Another theme could be adventure, where the two characters go on some sort of journey together.
A prevalent theme is the idea of Prussia being a strong and protective figure in the relationship. In lemon fanfictions, this protection can translate into a very physical and intimate way of showing care. Also, the cultural differences between Prussia's world and the reader's world (if it's a modern - day reader) can create interesting plot points and themes of cultural exchange within the relationship.
You could also try Fanfiction.net. Sometimes, you might have to dig a bit deeper as the tagging system might not be as precise as AO3. But if you search specifically for '2p Prussia x Reader', you're likely to find some interesting fanfics that explore different storylines and character dynamics.
Cultural exploration is another. Given the distinct cultures of Germany and Prussia, fanfics may explore how the reader experiences and learns about their cultures, like their cuisine, music, or art.
A very frequent theme is the exploration of cultural differences. Prussia has its own distinct culture compared to Germany, and when a reader is involved, it can be about the reader learning and adapting to these differences. Also, family - like relationships are common, as Prussia can be seen as an older 'brother' figure in some interpretations, and the stories might show how they all interact in a family - dynamic - like way. For instance, they could have family dinners or celebrations together, and the reader gets to be a part of it, which is really heartwarming to read about.
One common theme is cultural integration. Since Prussia has its own unique culture, there are often elements of Prussian traditions in the wedding, like certain types of music, food, or wedding attire. Another theme is the strong emotional bond between Prussia and the reader. It's about two people deeply in love coming together in a big celebration.
A big theme is also about acceptance. The reader, who may be different in some way, is accepted by Sully completely. For example, in some fanfictions, the reader might be a new kind of monster or have a unique ability. Sully's kind heart makes him open to the reader, and this acceptance forms the basis of their relationship. It also shows how they overcome any prejudices that might exist in their world.
One common theme is the clash of cultures. America is young and brash, while Prussia has a long and proud history. This contrast often leads to interesting interactions. Another theme is friendship or rivalry. They can be seen as competitors or as comrades depending on the story.
One common theme is the clash of personalities. Prussia is often depicted as bold and assertive while England is more reserved. Their interactions based on these differences are a big part of many fics.
A common theme is the exploration of their historical rivalry. Fanfictions often play with how they could overcome or at least manage this rivalry in different scenarios.